EP3047293B1

EP3047293B1 - Mri using a modified dixon sequence with reduction of fold-over artifacts

Info

Publication number: EP3047293B1
Application number: EP14766223.3A
Authority: EP
Inventors: Ivan PEDROSA; Ananth MADHURANTHAKAM; Ivan Dimitrov
Original assignee: Koninklijke Philips NV; University of Texas System
Current assignee: Koninklijke Philips NV; University of Texas System
Priority date: 2013-09-16
Filing date: 2014-09-02
Publication date: 2020-08-05
Anticipated expiration: 2034-09-02
Also published as: CN105556327B; JP2016530048A; CN105556327A; US20160231406A1; JP6415573B2; EP3047293A1; US10408904B2; WO2015036895A1

Description

The present system relates to a magnetic resonance imaging (MRI) system for acquiring dynamic contrast enhanced (DCE) images of an abdomen or pelvis of a patient, for example, with acquisition times within a breathhold and, more particularly, to a magnetic resonance imaging (MRI) system for performing a DCE image acquisition while achieving homogeneous fat suppression and out-of field-of-view (FOV) signal suppression within a breath-hold scan time.
Magnetic Resonance Imaging (MRI) to acquire images of an abdomen and/or pelvis of a patient presents many challenges such as those due to a requirement of high spatial resolution combined with a constraint of a short acquisition time which is within a breath-hold of the patient (e.g., about 15-25 seconds). For a given spatial resolution, a scan time is directly proportional to a size of the field of view (FOV) and, hence, a reduced FOV can increase the spatial resolution within a reasonable breath-hold scan time.
To acquire images of the abdomen and/or pelvis, patients are often placed in magnetic resonance (MR) scanners with their arms above their head to minimize wrap around artifacts along the right-left (RL) direction with a reduced FOV. In certain clinical cases, such as in MR Enterography (MRE), patients may be debilitated and imaging portions of the abdomen and/or pelvis (i.e. torso) of the patient with the patient's arms above their head is not always possible due to various reasons, such as patient's inability to keep arms above their head, and use of medical devices (e.g., monitoring devices, lines, sensors, tubes, etc.) which maybe attached to the patient. In such instances, imaging with the arms positioned down along each the side of the patient may be necessary and a large FOV is typically used to avoid wrap around artifacts, which result in longer acquisition times. Parallel imaging methods can be used to accelerate the acquisition and reduce the total scan times.
However, in a typical scan when a patient's arms are positioned besides the patient, a large FOV combined with high acceleration factors usually results in acquired images having undesirable artifacts. These artifacts are due to signals originating outside of the FOV, particularly, signals due to the arms of the patient which are outside of the FOV. Accordingly, a Rotated Slab Excitation (ROSE) approach, in which a 3D volume is encoded in the coronal plane while volume excitation is switched from an anterior-posterior (AP) direction to an RL direction (e.g., a sagittal excitation), can be used to suppress signals which originate outside of the FOV. However, high-resolution ROSE approach with good out-of-FOV signal suppression often leads to increased minimum echo times (TEs) due to the use of prolonged radiofrequency (RF) pulses. Unfortunately, when this ROSE approach is combined with chemical-shift approach for fat separation, which is often a confounding tissue and needs to be suppressed for improved delineation of the underlying structures, a fat/water separation process fails due to a violation of optimum echo times (TE) which are increased due to the increase in the minimum echo times (TEs) required by the ROSE approach. For example, a typical ROSE approach requires a TE of 1.5 ms for resolution of 1 x 1 mm, which exceeds the optimal TE of 1.2 ms required by the fat/water separation algorithm at 3 Tesla field strength.
US 2012/301000 A1 discloses a method of performing coronary magnetic resonance angiography with signal separation for water and fat. Coronary magnetic resonance angiography datasets are acquired using multi-echo Dixon acquisition. A Dixon reconstruction technique is employed to obtain separate water and fat images.
Jing Yuan et al. (Quantitative Imaging in Medicine and Surgery, 1 March 2012, pages 21-32) describe a technique for temperature mapping using proton resonance frequency (PRF)-based MR thermometry. In this context, imaging of a reduced field-of-view using 2D RF pulses combined with "Fourier encoding of the overlaps using the temporal dimension (UNFOLD)" is disclosed.
The system(s), device(s), method(s), user interface(s), computer program(s), processes, etc. (hereinafter each of which will be referred to as system, unless the context indicates otherwise), described herein address problems in prior art systems.
In accordance with embodiments of the present system, there is disclosed a magnetic resonance imaging (MRI) system according to claim 1. The system includes at least one controller which: performs a mDIXON sequence for fat/water separation within a field-of-view (FOV) which lies within a scanning volume, the mDIXON sequence may be performed in the coronal direction; performs a rotated slab excitation sequence for volume selection to exclude portions of a subject under exam (e.g., a human, an animal, a phantom, etc., each of which for the sake of clarity will be commonly referred to as a patient or subject unless the context indicates otherwise) which are within the scanning volume and outside of the FOV so as to reduce, prevent, and/or suppress (hereinafter each of which may be commonly referred to as suppress, unless the context indicates otherwise) foldover artifacts which originate from the excluded portions of the patient, wherein the rotated slab excitation sequence encodes the scanning volume in a coronal plane and performs volume excitation based upon minimum-phase radio-frequency (RF) pulses in a sagittal plane; and acquires echoes for reconstructing an image. The use of minimum-phase RF pulses for volume excitation allows the echoes to be acquired at substantially optimal echo times in the mDIXON sequence. The excluded portions of the patient may include the patients, arms, hands, fingers, etc., each of which will be commonly referred to as arms for the sake of clarity unless the context indicates otherwise. The method may provide for parts of the skin, subcutaneous fat, and selected lateral parts of the internal organs to be excluded, without introducing fold-over artifacts. In accordance with yet further embodiments of the present system, the at least one controller may acquire the echo information while arms of the patient are within the scanning volume and positioned at the sides of the torso of the patient. The MRI system may further include a support movably controlled by the at least one controller and which is configured to position the patient to scanning position relative to the scanning volume. Further, it is envisioned that the mDIXON and rotated slab excitation sequences and the image acquisition may be performed substantially within a twenty second time interval with significantly high spatial resolution. Moreover, the minimum-phase RF pulses may be configured to reduce excitation of the excluded portions of the patient.
In accordance with yet other embodiments of the present system, there is disclosed a method of reconstructing images obtained by an MR imaging (MRI) system according to claim 6.
In accordance with other embodiments of the present system, there is disclosed a computer program stored on a non-transitory computer readable memory medium according to claim 11.
The invention is explained in further detail, and by way of example, with reference to the accompanying drawings wherein:

FIG. 1 is a flow diagram that illustrates a process performed by an imaging system in accordance with embodiments of the present system.
FIG. 2 shows a pulse sequence formed in accordance with embodiments of the present system;
FIG. 3A shows an image acquired using a phantom and application of a small FOV;
FIG. 3B shows an image of a portion of the phantom acquired using symmetric long RF pulses which result in an excellent out-of-volume signal suppression but poor mDIXON fat/water separation;
FIG. 3C shows an image of a portion of the phantom acquired using shorter symmetric pulses which improve mDIXON reconstruction but cause poor out-of field-of-view (FOV) suppression with a standard ROSE method;
FIG. 3D shows an image of a portion of the phantom acquired in accordance with embodiments of the present system;
FIG. 4A shows an image of a patient acquired using a small coronal FOV;
FIG. 4B shows an image of the patient acquired using a small FOV;
FIG. 4C shows an image of the patient acquired in accordance with embodiments of the present system; and
FIG. 5 shows a portion of a system (e.g., peer, server, etc.) in accordance with an embodiment of the present system.

The following are descriptions of illustrative embodiments that when taken in conjunction with the following drawings will demonstrate the above noted features and advantages, as well as further ones.
In accordance with embodiments of the present system, an MRI system is disclosed which uses minimum-phase RF pulses that provide enhanced out-of FOV suppression without increasing echo times (TEs) so that the echo times (TEs) are substantially optimal and do not exceed upper threshold values of approximately 2.2 ms for the first and 4.4 ms for the second echo, at 1.5T; and 1.2 for the first and 2.4 ms for the second echo at 3T. This minimum-phase RF pulse approach combined with a chemical-shift technique allows for the acquisition of data at optimum echo times (TEs) which are configured to provide uniform fat/water separation. In accordance with embodiments of the present system, the minimum-phase RF pulses provide excellent out of FOV suppression and enable the use of very high acceleration factors in the RL direction to reduce scan times. The combination of all the above-described approaches provides for an MR imaging technique for acquiring MR images with high spatial resolution within breath hold acquisition times and uniform fat/water separation. Further, these images can be acquired while the patient's arms are positioned at their side (e.g., on the respective sides of the patient's torso) for enhanced patient comfort.
FIG. 1 is a flow diagram that illustrates a process 100 performed by an imaging system in accordance with embodiments of the present system. The process 100 is performed using one or more computers communicating over a network and obtains information from, and/or stores information to one or more memories which may be local and/or remote from each other. The process 100 includes one or more of the following acts. Further, one or more of these acts may be combined and/or separated into sub-acts, if desired. The image information includes k-space image information. In operation, the process starts during act 101 and then proceeds to act 103.
During act 103, the process positions a patient within a bore of an MRI system. Accordingly, the process controls actuators of a support table (e.g., a patient support table) to position the patient so that a desired portion of the subject under test (e.g., a torso of a human patient in the present embodiments) is aligned within the bore of the MR system. More particularly, the torso should be positioned within scanning volume of the MRI such that the torso is situated within a field-of-view (FOV), as will be discussed below. The MRI system may include sensors which may provide information indicative of positions of one or more portions of the support table and/or patient relative to the bore of the MRI system. The process may obtain positioning information from a memory of the system (e.g., in accordance with a test type (e.g., torso, an abdomen, a pelvis, and/or portions thereof)) and/or from a user, if desired. After completing act 103, the process continues to act 105.
During act 105, the process performs a rotated slab excitation sequence (e.g., see, R2) to suppress foldover artifacts from portions of the patient which lie outside of the FOV but are within the scanning volume such as the arms of the patient, parts of the skin, subcutaneous fat, and selected lateral parts of the internal organs which, in the present embodiments are assumed to be positioned at the sides of the torso of the patient. During the performance of the rotated slab excitation sequence, the process generates the rotated slab excitation sequence and/or transmits the rotated slab excitation sequence to one or more coils (e.g., the gradient, RF coils, and/or other coils) of the MRI system so as to be output by the corresponding coils. The rotated slab excitation sequence encodes the volume (e.g., a three-dimensional (3D) volume) in a coronal plane while volume excitation is switched from the anterior-posterior (AP) direction to the right-left (RL) direction. In accordance with embodiments of the present system, the volume excitation is set to the RL direction (sagittal) throughout the entire sequence. In other words, the volume excitation includes a sagittal excitation. This provides for volume selection that may exclude undesired portions of the patent at the sides of the torso such as the patient's arms hands, etc. Further, the sagittal excitation includes RF pulses which suppress (e.g., suppress, reduce, or entirely prevent) excitation of the undesired portions of the patient such as the arms (hands, etc.). The minimum-phase RF pulses provide for a sharp transition region with minimum sideband excitation ripples, as not to excite any of the body structures (arm, subcutaneous fat, etc.). This way, substantially no undesired anatomy is excited and foldover artifacts are prevented or substantially reduced. After completing act 105, the process continues to act 107.
During act 107, the process performs a chemical-shift sequence to generate a large field-of-view (FOV) for acquisition of echo information from the desired portion of the patient within a desired period of time such as a breath-hold (e.g., about 15-25 seconds, however other values or ranges of values are also envisioned). The chemical-shift sequence includes a chemical-shift based gradient echo acquisition (e.g., a 3D Fast Field Echo (FFE) mDIXON) (see, R1) sequence to generate large FOV dynamic-contrast-enhanced (DCE) acquisitions (e.g., see, act 109) of the desired region (e.g., the torso, an entire abdomen, a pelvis, etc.) of the patient within a single breath-hold (e.g., about 15-25 seconds). The 3D FFE mDIXON sequence for fat/water decomposition does not prolong scan time and is substantially unaffected by B_o inhomogeneity, which results in substantially uniform fat suppression throughout large FOVs such as the current FOV. Further, during performance of the chemical-shift sequence, the process generates the chemical-shift sequence and/or transmits the sequence to one or more coils (e.g., the gradient and/or RF coils) of the MRI system. After completing act 107, the process continues to act 109.
Referring back to acts 105 and 107, the rotated slab excitation and mDIXON methods performed by embodiments of the present system may be referred to as an mDIXON Acquisition for Torso Imaging with Selective Sagittal Excitation (mATISSE) and may provide high-resolution, homogenous fat-suppressed acquisitions (e.g., of echo information for reconstructing images) of the abdomen and pelvis of a patient with a FOV tightly adjusted (e.g., selectively controlled) to the torso and suppressing information from the arms at the side of the torso so as to be free of foldover artifacts due to the arms.
During act 109, the process acquires echo information suitable to reconstruct, at least in part, one or more images of the patient. The echo information is processed by the process using any suitable method or methods to generate image information for reproducing at least fat and/or water images. The echo information is obtained within an optimum echo time for fat/water separation. In accordance with embodiments of the present system, the optimum echo times may be as short as possible. For example, in accordance with some embodiments, the optimum echo times may be at most approximately 2.2 ms for the first echo and 4.4 ms for the second echo, at 1.5T; and 1.2 for the first echo and 2.4 ms for the second echo at 3T, if desired. However, other echo times are also envisioned. After completing act 109, the process continues to act 111.
During act 111, the process reconstructs the image information in accordance with embodiments of the present system so as to obtain reconstructed image information. The reconstruction is performed using a commonly known mDIXON reconstruction technique. The image reconstruction is performed using any suitable application such as multi-peak, fat-water separation based on chemical shift imaging or the like. After completing act 111, the process continues to act 113.
During act 113, the process renders the reconstructed image information on, for example, a display of the system so that a user may view the reconstructed image. The process may further provide a user interface (UI) with which a user may interact to change viewing parameters, etc., enter information (e.g., notes, commands, etc.). The process may process inputs of the user in real time and render corresponding results in real time. After completing act 113, the process continues to act 115.
During act 115, the process updates history information stored in a memory of the system in accordance with raw information (e.g., echo information), reconstructed image information (e.g., a fat image, a water image, etc.), results, etc., of the present process. For example, the process stores information that it uses and/or generates (e.g., results of determinations, MR image information, settings, parameters, day, date, time, etc.) in a memory of the system for later use, analysis, and/or other processing. The information is stored in association with a name of a corresponding patient, a name of a user (e.g., a professional such as a radiologist), a FOV, a ROI, etc. Further, in some embodiments, the process may store information determined and/or calculated by the process such as various extracted image information, the transformed image information, etc., for later use. Accordingly, for example, the process may store the reconstructed image information in a memory of the system for later use. After completing act 115, the process continues to act 117 where it ends.
Thus, embodiments of the present system use a minimum-phase RF pulse with a rotated slab excitation method. Further a combination of the rotated slab excitation method uses a minimum-phase RF pulse with a chemical-shift technique for uniform fat/water separation. Moreover, the use of very-high acceleration factors in the right-left direction may be afforded by excellent out-of FOV suppression by the minimum-phase RF pulse.
FIG. 2 shows a pulse sequence diagram 200 formed in accordance with embodiments of the present system. The sequence includes one or more of an excitation along the sagittal plane (e.g., same plane as the phase-encoding plane) 202, a standard or a minimum-phase RF pulse 204, and an acquisition of two echoes 206 at optimal echo times as required for mDIXON reconstruction.

Experimental Results:

Experimental results will now be described with reference to FIGs. 3A through 4C. The experimental results were obtained using a 1.5T wide-bore (70 cm) Ingenia scanner (by Philips™ Medical™). Embodiments of the present system provide enhanced speed and fat-suppression ability of chemical-shift based gradient echo acquisition (3D FFE mDIXON) to generate large-FOV, DCE acquisitions of the entire abdomen and pelvis of a patient within a single breath-hold. Phantom results are shown in FIGs. 3A through 3D, and images of a patient are shown in FIGs. 4A through 4C. Further, no radio-frequency (RF) blankets were used in the acquisition of the images of FIGs. 3A through 4C.
FIG. 3A shows an image 300A acquired using a phantom and application of a small FOV. Frame 302A surrounds the small field-of-view (FOV) centered on Frame 304A. FIG. 3B shows an image 300B of a portion of the phantom acquired using symmetric long RF pulses which result in excellent out-of-volume signal suppression but with incomplete fat/water separation due to the long echo times required by the long symmetric RF pulse. Frame 306B surrounds an ROI that was used for evaluation of the level of fold-over artifact suppression FIG. 3C shows an image 300C of a portion of the phantom acquired using shorter RF pulses than the symmetric RF pulses used on Fig 3B. This improves the mDIXON reconstruction but causes poor out-of FOV suppression when using the ROSE method. FIG. 3D shows an image 300D of a portion of the phantom acquired in accordance with embodiments of the present system. The image 300D was acquired using stretched minimum-phase RF pulses in accordance with embodiments of the present system. These stretched minimum phase RF pulses generate both excellent ROSE artifact suppression and mDIXON fat suppression.
FIG. 4A shows an image 400A of a patient and the position of a small coronal FOV 402A that excludes the arms 401A. The small coronal FOV 402A allows shorter acquisition times but leaves arms 401A of the patient outside of the FOV. FIG. 4B shows an image 400B of the patient acquired using a small FOV. Artifacts 403A (e.g., foldover artifacts) are generated by the arms 401A when right-left (RL) phase encoding is applied with the small FOV. FIG. 4C shows an image 400C of the patient acquired in accordance with embodiments of the present system. The image was obtained using a combined sagittal three-dimensional (3D) excitation based upon a stretched minimum-phase RF pulses and coronal mDIXON readout which provides for a small FOV with excellent outer-volume signal elimination and proper fat suppression.
Accordingly, embodiments of the present system provide MR imaging methods for acquiring images with high spatial resolution within breath-hold acquisition times and with uniform fat/water separation. The images may be acquired with patients comfortably positioned with their arms beside their bodies or with their arms in a downward position. Further benefits of the present system include the avoidance of scan-session interruption, which interruption is typically due to the need to pull a patient from a scanner bore to rest a patient's upward positioned hands. Further benefits of the present system include a reduced set up time when compared with typical methods which position a patient's hands in a downward position as radio-frequency (RF) shielding does not have to be placed about the patient's arms to suppress undesirable signals.
FIG. 5 shows a portion of a system 500 (e.g., peer, server, etc.) in accordance with embodiments of the present system. For example, a portion of the present system includes a processor 510 (e.g., a controller) operationally coupled to a memory 520, a display 530, sensors 540, RF transducers 560, magnetic coils 590, and a user input device 570. The memory 520 may be any type of device for storing application data as well as other data related to the described operation. The application data and other data are received by the processor 510 for configuring (e.g., programming) the processor 510 to perform operation acts in accordance with the present system. The processor 510 so configured becomes a special purpose machine particularly suited for performing in accordance with embodiments of the present system.
The operation acts may include configuring an MRI system by, for example, controlling optional support actuators, the magnetic coils 590, and/or the RF transducers 560. The support actuators may control a physical location (e.g., in x, y, and z axes) of a patient, if desired. The magnetic coils 590 may include main magnetic coils, and gradient coils (e.g., x-, y-, and z-gradient coils) and are controlled to emit a main magnetic field and/or gradient fields in a desired direction and/or strength. The controller controls one or more power supplies to provide power to the magnetic coils 590 so that a desired magnetic field is emitted at a desired time. The RF transducers 560 are controlled to transmit RF pulses at the patient and/or to receive echo information therefrom. A reconstructor processes received signals such as the echo information and transform them (e.g., using one or more reconstruction techniques of embodiments of the present system) into content which includes image information (e.g., still or video images (e.g., video information)), data, and/or graphs that can be rendered on, for example, a user interface (UI) of the present system such as on the display 530, a speaker, etc. Further, the content is then be stored in a memory of the system such as the memory 520 for later use. Thus, operation acts includes requesting, providing, and/or rendering of content such as, for example, reconstructed image information obtained from the echo information. The processor 510 renders the content such as video information on a UI of the system such as a display of the system.
The user input 570 may include a keyboard, a mouse, a trackball, or other device, such as a touch-sensitive display, which may be stand alone or be a part of a system, such as part of a personal computer, a personal digital assistant (PDA), a mobile phone (e.g., a smart phone), a monitor, a smart- or dumb-terminal or other device for communicating with the processor 510 via any operable link. The user input device 570 may be operable for interacting with the processor 510 including enabling interaction within a UI as described herein. Clearly the processor 510, the memory 520, display 530, and/or user input device 570 may all or partly be a portion of a computer system or other device such as a client and/or server.
The methods of the present system are particularly suited to be carried out by a computer software program, such program containing modules corresponding to one or more of the individual steps or acts described and/or envisioned by the present system. Such program may of course be embodied in a computer-readable medium, such as an integrated chip, a peripheral device or memory, such as the memory 520 or other memory coupled to the processor 510.
The program and/or program portions contained in the memory 520 configure the processor 510 to implement the methods, operational acts, and functions disclosed herein. The memories may be distributed, for example between the clients and/or servers, or local, and the processor 510, where additional processors may be provided, may also be distributed or may be singular. The memories may be implemented as electrical, magnetic or optical memory, or any combination of these or other types of storage devices. Moreover, the term "memory" should be construed broadly enough to encompass any information able to be read from or written to an address in an addressable space accessible by the processor 510. With this definition, information accessible through a network is still within the memory, for instance, because the processor 510 may retrieve the information from the network for operation in accordance with the present system.
The processor 510 is operable for providing control signals and/or performing operations in response to input signals from the user input device 570 as well as in response to other devices of a network and executing instructions stored in the memory 520. The processor 510 may include one or more of a microprocessor, an application-specific or general-use integrated circuit(s), a logic device, etc. Further, the processor 510 maybe a dedicated processor for performing in accordance with the present system or may be a general-purpose processor wherein only one of many functions operates for performing in accordance with the present system. The processor 510 may operate utilizing a program portion, multiple program segments, or may be a hardware device utilizing a dedicated or multi-purpose integrated circuit.
Embodiments of the present system may provide fast imaging methods to acquire and reconstruct images. Suitable applications may include imaging systems such as magnetic resonance imaging (MRI) systems and the like which require: a short acquisition time and high resolution while providing homogeneous fat suppression and out-of-FOV signal suppression. Accordingly, embodiments of the present system provide for a high-resolution, breath-held DCE acquisition clinical MRE protocol which can be used upon patients who are comfortably positioned with their arms along their side while achieving homogeneous fat suppression and out-of-FOV signal suppression.

REFERENCES:

References 1-2 listed below are referred to using reference numerals R1 and R2, respectively, throughout the specification. For example, R1 may make reference to the first reference (e.g., by Ma, J).
1. Ma, J., MRM 52(2):415-9, 2004.
2. Brau, A. et al., Proc. ISMRM 16, 502, 2008.

Claims

A magnetic resonance imaging (= MRI) system (500), the system comprising at least one controller (510) which is configured to:
perform a rotated slab excitation sequence for volume selection to exclude portions of a subject under exam which are within a scanning volume and outside of a field-of-view (=FOV) so as to reduce foldover artifacts which originate from the excluded portions of the subject under exam, wherein the rotated slab excitation sequence performs volume excitation using minimum-phase radio-frequency (= RF) pulses in a sagittal plane and encodes the scanning volume in a coronal plane;

after performing the rotated slab excitation sequence for volume excitation, perform a mDIXON chemical-shift imaging sequence for fat/water separation within a FOV which lies within the scanning volume, wherein the mDIXON sequence includes the acquisition of echoes for reconstructing an image, whereby the use of minimum-phase RF pulses for volume excitation allows the echoes to be acquired at substantially optimal echo times.
The MRI system of claim 1, wherein the at least one controller (510) is configured to acquire the echo information while arms of the subject under exam are within the scanning volume and positioned at the sides of a torso of the subject under exam.
The MRI system of claim 2, further comprising a support movably controlled by the at least one controller and which is configured to position the subject under exam into scanning position relative to the scanning volume.
The MRI system of claim 1, wherein the controller is further configured such that the rotated slab excitation and mDIXON sequences are performed within a time interval of between 15 and 25 seconds.
The MRI system of claim 1, wherein the controller is further configured such that the minimum phase RF pulses reduce excitation of the excluded portions of the subject under exam.
A method of reconstructing images obtained by a magnetic resonance imaging (= MRI) system (500), the method performed by at least one controller (510) of the MR imaging system (500) and comprising acts of:
performing (105) a modified rotated slab excitation sequence for volume selection to exclude portions of a subject under exam which are within a scanning volume and outside of a field-of-view (FOV) so as to reduce foldover artifacts which originate from the excluded portions of a subject under exam, wherein the rotated slab excitation sequence performs volume excitation based upon minimum-phase radio-frequency (RF) pulses in a sagittal plane and encodes the scanning volume in a coronal plane;

after performing the rotated slab excitation sequence for volume excitation, performing (107) a mDIXON chemical-shift imaging sequence for fat/water separation within the FOV which lies within the scanning volume, wherein the mDIXON sequence includes the acquisition (109) of echoes for reconstructing (111) an image, whereby the use of minimum-phase RF pulses for volume excitation allows the echoes to be acquired at substantially optimal echo times.
The method of claim 6, wherein the echo information is acquired while arms of the subject under exam are within the scanning volume and positioned at the sides of a torso of the subject under exam.
The method of claim 6, further comprising an act of controlling, by the at least one controller of the MRI system, a support to position (103) the subject under exam to a scanning position within the scanning volume.
The method of claim 6, further comprising an act of performing the rotated slab excitation and mDIXON sequences and the image acquisition within a time interval of between 15 and 25 seconds.
The method of claim 6, further comprising an act of reducing the excitation of the excluded portions of the subject under exam using the minimum-phase RF pulses.
A non-transitory computer readable medium (520) comprising computer instructions which, when executed by a processor of a computer comprised in a magnetic resonance imaging (= MRI) system (500), control the MRI system to perform the method according to any one of claims 6-10.